The pup should be at-least 80 days old for best health when they grow up.
The parents need to be seen for temperamental issues, you can ask the breeder for the health records for parents as well.
The registration is a question for you to decide, its not a thumb rule to get the pet registered.
Vaccination papers need to be obtained/ seen before you zeroed down to pups.
Male or Female, it would depend on your need, Females are small is size as compared to males, all breed have different traits, please research and take your call.